I own a Cruiser but your question isn't getting a 'direct' answer and it's a simple calculation so...
The industry (cycling) uses the gear inch and a lot of hand waving to get some approximations. In Europe they use something called 'advantage' or something similar and it's closer to what you want but getting an actual cadence vs mph for any gear pairing is just simple arithmetic (I've got it in a spreadsheet for the asking its inputs are chainring teeth, cassette teeth, crank cycles per minute); here goes. My middle sprocket on the chainring has 42 teeth. Speed is important so we'll use the high gear on the cassette-11 teeth.
For every spin/cycle/stroke of the chainring the back wheel does 42/11 cycles (3.82 revolutions).
My back tire is 26 inches and for the sake of simplicity we'll use that as the true diameter. pi*d is the circumference (81.64 inches).
Every crank on the pedel/chainring moves the trike 3.82 * 81.64 inches (311.86 inches). Fifty crank cycles per minute (my average) is 50 * 311.86 inches (15593.24 inches). Sixty minutes in an hour is 60 * 15593.24 (935594.40 inches) traveled/hour.
One mile is 5280 feet, each foot 12 inches or 63360 inches/mile.
935594.4 inches per hour is 935594.4 / 63360 mph (14.77 mph))
Want the Excel Spreadsheet? firstname.lastname@example.org